Details of the tragedy were revealed during an inquest into the young care volunteer's death at Dorchester County Hall.

Miss Blackman, from Heanor, was spending a day at the beach with her father, 12-year-old brother Mitchell, his school friend, and Mr Carnell.

Charlotte's mother Rachel remained at their caravan park nearby.

Giving evidence at the hearing, Mr Carnell said the group inadvertently walked into the path of tragedy after deciding to return to camp along the beach.

"Within a minute, my attention was drawn to two small stones," he said.

"Almost immediately, I looked up at the cliff and saw half the cliff face fall a few metres from the sea."

Mr Carnell, who had been with Charlotte for several years, continued: "It happened so fast, it was the blink of an eye. We had no time to get out of the way.

"I grabbed Mitchell and ran a few metres into the sea. With that, a large dust cloud appeared and it was impossible to see for 20 seconds.

"I turned to the area where the cliff face fell, boulders the size of a hay stack. I couldn't see Charlotte at all.

"The height of the boulders from ground level was higher than 10ft. People approached and told us to get out of the way.

"It was complete chaos. I was in a panic and all I could think about was to get Charlotte out of there. I didn't want to stop until I found her.

"I was 10ft away from Charlotte at the time (of the landslide).

Image Caption:The Jurassic cliffs in Dorset where Charlotte was killed

"I remember seeing two little stones, no bigger than a 10p piece. Then the whole lot came down."

Asked by the coroner if there were any signs of cliff fall, Mr Carnell said: "There were a few boulders but they looked like they had been there for years."

Horrified eyewitnesses called emergency services while Miss Blackman's partner and her father desperately tried to pull her to safety.

Mr Blackman himself was also injured in the cliff fall.

He told onlookers concerned for his safety during the rescue attempts that if he was going to "go", it would be with his daughter.

There were conflicting accounts, as witnesses reported up to three different landslides along the beach before the one which killed Miss Blackman.

Her father, however, said he would not have taken his children along the beach if there had been evidence of recent landslides.

The death came a fortnight after Somerset couple Rosemary Snell, 67, and Michael Rolfe, 72, were killed in a landslide at the Beaminster Tunnel, less than 10 miles from Freshwater, following days of extremely heavy rainfall.

But the coroner heard evidence from a scientific expert that the weather may have had little impact on the fatal cliff fall which killed Miss Blackman.

Coroner Sheriff Payne told the hearing Miss Blackman's death could not have been predicted.

He said the National Trust appeared to be doing all it could to warn visitors of the dangers presented by the 100ft cliffs.

And he said there was not sufficient evidence to say if the weather had played a part in the landslide.

He had heard concerns that heavy rain in the county in the preceding weeks may have triggered large sections of the cliff to fall.

He said: "Sadly, Charlotte Blackman died as a result of an accident. It was a sudden act of nature that nobody could have predicted at that time."